How do the options in the Post Processing tab work?
Those two check boxes toggle using the compositor and sequencer.

If you are using any compositing nodes, then you will need to have the Compositing box checked.

If you are using the VSE for anything, then likewise you will need to have the Sequencer box checked.

If you are just rendering from a 3D scene, then you can uncheck both boxes.

Now most of the time you can safely leave both of them checked.
When the VSE is empty it will do nothing. However when the compositor is empty, and the Compositing box is checked, like your issue, the render will turn out blank.

See my answer for a bit more on the compositor's required nodes.